1. Field of the Invention
The present invention relates generally to signaling system and, more particularly, to selective signaling systems wherein one or more coded transmitters communicate with one or more receivers and cause actuation of only that receiver programmed to the transmitted code.
2. Description of the Prior Art
Remote control and signaling systems of various types have been available for quite some time. Examples of prior art systems can be found from the simplest remote control garage door openers to the most sophisticated enviromental control systems used for multiple building complexes to regulate everything from lighting to burglar alarms, fire detection systems, heating and colling systems, and telephone answering apparatus. Examples of remote control can also be found in the industrial environment where centralized control of many manufacturing and processing facilities and steps are today being provided in order to reduce manpower needs and high labor costs.
The conventionally available remote control signaling sytems have generally proven to be satisfactory for their intended purposes; however, they often exhibit a number of serious disadvantages and limitations which sometimes render the system totally unacceptable. For example, many medical applications for remote control and monitoring systems must meet stringent reliability and accuracy standards in order to protect the lives of the patients involved. Improper control or false triggering in such a system could have the gravest of consequences and thus cannot be tolerated.
Many prior art systems attempt to provide selectivity and prevent false triggering by tuning the receiver section to respond to incoming signals of only a single frequency. Second generation versions of this type of system may provide for discrimination of a multi-frequency signal; however, the provision of more than two or three descrete frequencies results in the system having considerable complexity and added costs. Naturally, the more complex the system, the greater its isolation from spurious signals. However, as one continues to make the system more complex, a point is reached where the economic disadvantages outweigh the advantages of increased selectivity. Unfortunately, this tradeoff has in the past been typically at a point below that which precludes all likely false responses, and many signaling systems have been found unsatisfactory for this reason.
Another serious drawback prevalent in prior art devices of this general type is their lack of flexibility and adaptability to different remote control and signaling situations. In that case, each individual remote control system has to be custom designed or modified to meet the requirements of the overall system to which it is adapted. If each major installation requires design modification by professional engineers, cost again become prohibitive. Furthermore, limited general applicability prevents these systems from being extensively advertised which has limited their widespread acceptance by the general public.
While the need for error-free, selective, remote control and signaling has been long recognized, there has heretofore been unavailable any system having substantial flexibility, considerable immunity to false triggering, adaptability to small, integrated circuit construction, and low initial costs and maintenace.